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Respiratory Function Tests

Respiratory Function Tests. Fiona Gilmour SHO 03/06/04. Respiratory Function Tests. Mechanical Function Spirometry Lung Volumes Diffusion Capacity Gas Exchange Function Arterial Blood Gases. Use?. Do not predict individual risk of pulmonary complications Smoking Exercise tolerance

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Respiratory Function Tests

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  1. Respiratory Function Tests Fiona Gilmour SHO 03/06/04

  2. Respiratory Function Tests • Mechanical Function • Spirometry • Lung Volumes • Diffusion Capacity • Gas Exchange Function • Arterial Blood Gases

  3. Use? • Do not predict individual risk of pulmonary complications • Smoking • Exercise tolerance • Type of surgery • Those who benefit pre-op • Equivocal clinical or CXR findings to aid Dx • Functional ability cannot be assessed eg Physically disabled • Thoracic resections - specific requirements • Most useful for monitoring response to therapy/ following progress of disease

  4. Validity depends on • Co-operation and technique of patient • Experience of operator • Quality of equipment • Various patterns overlap so difficult to interpret

  5. Spirometry

  6. Lung Volumes • VT = volume breathed in and out in relaxed breathing • IRV = extra volume that can be inhaled with maximum effort • ERV = extra volume expired with maximum effort • IRV+VT+ERV = Vital capacity (VC) • ERV+RV = Functional residual capacity (FRC)

  7. Spirometry 2 • FEV1 = volume exhaled in 1 second • FVC = total forced volume exhaled • FEV1/FVC% • PEF = Peak expiratory flow during forced expiration • All values compared to predicted values based on • Age • Sex • Height +/or weight • Race

  8. Spirometry 3 • Specific disease patterns can be seen based on these values • Obstructive • Restrictive • Normal FEV1/FVC is 80% • If obstructive picture found response to bronchodilators is measured

  9. Spirometry 4

  10. Expiratory Flow • Measured on spirometer or peak flow meter • Compared with predicted values • Reduced values indicate airflow obstruction • If diary kept indicates current fitness • Maximum flow rates at different stages of VC can also be measured • indicates small airway function • PEF <200L/min effective cough is difficult

  11. Diffusion Capacity • Carbon monoxide diffusing capacity (DLCO) is rate of transfer of CO from inspired gas to pulmonary capillary (transfer factor) • Indicates health of alveolar-capillary membrane • Useful for evaluation of Emphysema • Does not indicate gas exchange • Measured by single breath test • RV can be measured at the same time using Helium

  12. Relevance to Thoracic • Need to assess cardiorespiratory reserve • Can estimate post op lung function • Needs to be considered in context of patients health and proposed resection • 3 Groups • Fit, good exercise tolerance, normal spirometry • major med probs, min ex tol, grossly abnormal spirometry • Mod coexisting disease, reduced ex tol, abnormal spirometry

  13. Cont. • Post op estimate FEV1 <800L or FVC < 15ml/kg increases risk, difficult to cough and may need ventilation • Post op estimate = Pre op value x (5 - no.lobes resected) / 5 • Goal is post op value FEV1 > 35% predicted • Minimum pre op FEV1 • Pneumonectomy >55% • Lobectomy >40% • Wedge >35%

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